1. Field of the Invention
The present invention relates to an energy dispersive X-ray detector for use in an energy dispersive X-ray analyzer or an X-ray fluorescence thickness gauge, etc.
2. Description of Related Art
Detectors such as proportional counters, cooled Si-PIN diode detection elements and Si(Li) detection elements are used in energy dispersive X-ray analyzers and X-ray fluorescence thickness gauges of the related art.
Further, semiconductor radiation detection elements employing Ge semiconductor radiation detection elements or compound semiconductors such as CdTe or CdZn etc. are also employed with comparatively high-energy X-rays or high-energy radiation detection.
The proportional counter is one form of a gas-filled detector and one important application is detecting and performing spectral measurements for relatively low energy X-rays. For example, with a proportional counter employing Xe gas, the absorption efficiency with respect to incident X-rays is extremely high up to approximately 10 keV and the absorption rate is lower with respect to high-energy X-rays of greater than 10 keV but an effective response levels off at approximately 100 keV. Further, the resolution of the MnKα lines (5.9 keV) is approximately 10%. Proportional counters are therefore utilized in X-ray fluorescence thickness gauges because of the broadness of the detectable energy range, appropriateness of the resolution, and good detection efficiency.
Si-PIN diode detectors use ion injection methods and optical lithographic methods as a manufacturing method. Surface leakage current that causes resolution to deteriorate can therefore be made small because it is easy for deactivation due to oxidation to take place. Si-PIN diode detectors are possible to detect approximately 200 eV at the half-width of the MnKα line (5.9 keV) using a Peltier element etc. cooled to minus a few tens of degrees centigrade. The detection efficiency for X-rays of approximately 20 keV or more is therefore extremely poor because an i-layer, which is sensitive layer, cannot be made thick due to limitations with respect to purity of the Si semiconductor. However, because a large scale cooling system such as a liquid nitrogen cooling system etc. is not required and size of the detector itself is small, these are utilized in small-type X-ray fluorescence analyzers such as portable X-ray fluorescence analyzers.
Si(Li) detection elements are one type of p-i-n type structure detection elements composed of Si semiconductor and have the feature that sensitive layers a few millimeters thick are obtained by Li drift in p-type Si semiconductor. Detection efficiency is therefore even high for high-energy X-rays. It is also possible to realize approximately 130 eV at the half-width of the MnKα line (5.9 keV). However, in order to operate at a high level, it is necessary to provide cooling to approximately −100 degrees centigrade using liquid nitrogen or a pulse-tube freezer, etc.
Detection elements utilizing compound semiconductors such as CdTe or CdZnTe used as high energy radiation detectors having high radiation absorption capabilities have a sufficiently large band gap and can therefore operate at normal temperatures. However, the band gaps of these semiconductors are large compared to that of Si. The resolution obtained using the Peltier element even when cooling down to a few tens of degrees centigrade is therefore approximately 400 eV at the half-width of the MnKα line (5.9 keV).
The following three items are the main requirements regarding performance of radiation detectors used in energy dispersive X-ray fluorescence analyzer devices or film thickness gauges.    (1) Good energy resolution constituted by the ability to separate and identify fluorescent X-rays of neighboring energies.    (2) High detection efficiency with respect to a broad energy range of radiation.    (3) Straight forward maintenance.
Of the four types of detectors given in the related art, detectors employing Si(Li) semiconductors are radiation detectors capable of responding to the performance requirements described in (1) and (2). However, these require cooling systems such as liquid nitrogen systems which are difficult to maintain. In the case of a proportional counter and CdTe or CdZnTe, the cooling system can be simplified and detection efficiency with respect to high energies is high, but resolution is inferior. The cooling system can also be simplified for Si-PIN diode detectors and a certain degree of resolution can be attained, but with this configuration the detection efficiency is low for high-energy radiation.
As described above, when the four types of detector are used independently, it is difficult to fulfill all of the requirements. Devices have therefore employed one type of detector in line with the application up until this time.